1. Field of the Invention
This invention relates to a flame retardant for halogen-containing vinyl resins in which antimony pentoxide is contained as a main component, more specifically to a fame retardant for halogen-containing vinyl resins in which antimony pentoxide (Sb.sub.2 O.sub.5) is contained as a main component and which does not impair the transparency of the thermal stability of vinyl chloride resins.
2. Background Information
The halogen-containing vinyl resin itself has excellent fame retardancy, but a so-called flexible vinyl chloride resin plasticized with a plasticizer such as dioctyl phthalate and a halogen-containing vinyl resin blended with a combustible resin arc easily burnt. With regard to flexible vinyl chloride products such as leathers, hood cloths, wire-covering materials, films and sheets which are widely utilized as interior materials for automobiles, electrical and electronic parts, and architectural materials, or rigid vinyl chloride products blended with a reinforcing material against shock, it is especially essential to provide flame resistance.
In order to provide these resins with the flame resistance, a variety of flame retardants have been used. Examples of the flame retardants which are used include inorganic materials such as antimony trioxide (Sb.sub.2 O.sub.3), sodium antimonate, aluminum hydroxide, zirconium oxide, zinc borate and borax as well as organic materials such as tricresyl phosphate, trichloroethyl phosphate and chlorinated paraffins. Further, organic flame retardants containing bromine are also employed in rare cases. These flame retardants mentioned above have some advantages and disadvantages from the viewpoints of flame-resisting effect, transparency, thermal stability, weather resistance, cold resistance, bleed/bloom resistance and the like.
Antimony trioxide displays an extremely great opacifying effect, since it generally has a particle diameter of 0.5 to 10 .mu.m or so, a large refractive index and a small light transmittance. Therefore, the transparency which is the greatest feature of the halogen-containing vinyl resin will be completely lost, if the above-mentioned antimony trioxide is mixed with the resin. Further, when a pigment is added to the vinyl resin containing the antimony trioxide with the intention of coloring, a great deal of the pigment is required because of this opacifying effect, and kinds of obtainable colors are disadvantageously limited. In order to overcome these drawbacks, it has been suggested to excessively lessen the particle diameter of the antimony trioxide (Japanese Patent Publication No. 7170/-1971) and to conversely increase the particle diameter by single crystallization. Both of them contemplate improving the light transmittance. In the case of the former, the transparency can remarkably be enhanced, but if the pigment is added, the opacifying function will be heightened, the thermal stability also will become poor, and the manufacturing cost will rise. In the case of the latter sufficient transparency cannot be obtained. Inorganic materials such as aluminum hydroxide, zirconium oxide, zinc borate and borax are poorer in the flame-resisting effect than antimony trioxide, and have the behavior of losing the transparency of the resin like the antimony trioxide. A phosphorous plasticizer such as tricresyl phosphate and a chlorinated paraffin which have no behavior of losing the transparency but which have a plasticizing action are poorer in the flame-resisting effect than the antimony trioxide, therefore they must be added in greater amounts. As a result, bleeding will tend to occur and the cold resistance will deteriorate.
Antimony pentoxide is a flame retardant which is applicable to the halogen-containing vinyl resin which does not cause transparency of the resin to be lost (Journal Coated Fabric, Vol. 11, 1982, p. 137). This flame retardant is antimony pentoxide tetrahydrate which is prepared by bringing an antimony pentoxide sol (its particle diameter ranges from 20.times.10.sup.-3 to 100.times.10.sup.-3 .mu.m) into a powdery form with the aid of spray drying or the like. As for this antimony pentoxide tetrahydrate, the refractive index is small and primary particles are extremely fine. Therefore, the antimony pentoxide tetrahydrate has a great light transmittance, which fact indicates that the transparency of the resin is very good. This antimony pentoxide, however, has the drawback of worsening the thermal stability of the resin.
For the purpose of climinating this drawback, it has been suggested to make use of a Ba-Cd-Zn stabilizer or a tin mercaptide stabilizer. However, these stabilizers cannot be practically used, because of the formation of harmful cadmium and the bleed/bloom in the case of the Ba-Cd-Zn stabilizer, and because of a bad weather resistance in the case of the tin mercaptide stabilizer.
The present inventors have considered that the above problems would be caused because the antimony pentoxide which is obtained by subjecting antimony pentoxide sol to spray drying has strong cation exchangeability and it attracts the metal which is to be used as a stabilizer for the halogen-containing vinyl resin to the antimony pentoxide particles so that thermal stability of the halogen-containing vinyl resin becomes bad and practical application becomes impossible. Thus, the present inventors have proposed an antimony pentoxide type flame retardant which can overcome the above problems in Japanese Provisional Patent Publication No. 58453/1985 (which corresponds to U.S. Pat. No. 4,608,198).
That is, the above problems, particularly thermal stability can be greatly improved by antimony pentoxide containing an alkali metal, an alkaline earth metal and/or zinc, lead, and further an organic acid, a phosphoric acid and/or alkali phosphate.
However, in the improved antimony pentoxide type flame retardant, if an added amount is increased to improve flame retardancy, it can be clarified that it has a tendency that transparency, thermal stability and weather resistance are lowered.
The use of perchlorate to improve the thermal stability of a vinyl chloride resin has been known in the art as described in Japanese Provisional Patent Publication No. 203657/1985 ,(Chemical Abstracts, Vol. 104, 169513w).
Japanese Patent Application No. 110307/1987, filed May 6, 1987, published on November 15, 1988 as Unexamined Publication No. 277259/1988 concerns a flame retardant comprising antimony pentoxide, an alkyl metal compound, at least one compound of an alkaline earth metal, zinc or lead, perchloric acid and optionally organic acid and phosphoric acid.
In recent years, accompanying diversification of demand for the halogen-containing vinyl resin, a demand for the flame retardant halogen-containing vinyl resin having excellent transparency and coloration has increased more and more.
The present inventors have conducted intensive studies to resound to such a demand and to provide an antimony pentoxide type flame retardant which is more excellent in transparency and which does not lower various properties such as thermal stability and weather resistance.
Since the surface of antimony pentoxide colloid is acidic, it has a property to strongly bound with an organic base such as an amine, etc., so that by combining a hydrophobic amine, the antimony pentoxide colloid becomes hydrophobic. This hydrophobic antimony pentoxide colloid is dispersed in a plasticizer such as dioctyl phthalate (DOP) extremely well. Accordingly, the present inventors have considered that a flame retardant obtained by preventing the ion exchangeability of the antimony pentoxide and making the antimony pentoxide colloid a hydrophobic colloid which can be dispersed in the halogen-containing vinyl resin in the form of an extremely uniform colloid, whereby the halogon-containing vinyl resin can be made highly transparent to accomplish the present invention.